1. Field of the Invention
The present invention relates to a deinking composition to be used for the reclamation of waste papers such as newspapers and magazines. More particularly, the present invention relates to a deinking composition whereby a good defoaming property of flotation reject can be achieved and a deinked pulp which is little contaminated with total remaining ink can be obtained by deinking, for example, newspapers and magazines by flotation, washing or a combination thereof.
2. Description of the Related Art
It has been the practice to reclaim waste papers including newspapers, magazines and waste OA papers. Recently the effective utilization of waste papers has become more and more important in conjunction with the problems of the global environment such as the conservation of forest resources and refuse disposal. Further, it has been attempted to utilize a deinked pulp as a pulp of a higher rank, for example, to reclaim newspapers for use in making a paper of intermediate grade.
On the other hand, recent improvements in printing techniques, printing systems and printing ink compositions have made it difficult to deink waste papers. In order to facilitate deinking, therefore, attempts have been made to improve deinking devices and deinking procedures. In order to remove inks and other impurities from waste papers, a deinking composition which comprises alkaline agents such as caustic soda, sodium silicate, sodium carbonate and sodium phosphate, bleaching agents such as hydrogen peroxide, hydrosulfites and hypochlorites, and sequestering agents such as EDTA and DTPA, and deinking agents, either alone or in the form of a mixture thereof, including anionic surfactants such as alkylbenzenesulfonates, higher alcohol sulfates (or half esters of higher alcohols with sulfuric acid (ROSO.sub.3 M)), .alpha.-olefinsulfonates and dialkyl sulfosuccinates, nonionic surfactants such as ethylene oxide adducts of higher alcohols, ethylene oxide adducts of alkylphenols, ethylene oxide adducts of fatty acids and alkanolamides, has been used. Although these deinking compositions show excellent foaming properties in the flotation process, their abilities to collect ink are limited. In the washing method, on the other hand, they are poor in detergency and, furthermore, the good foaming properties thereof cause troubles in the effluent disposal step. As a result, only a deinked pulp of low grade can be obtained by using these deinking compositions. Further, a pulp of a high whiteness, if obtained, is contaminated with a large amount of total remaining ink, which restricts the utilization of the deinked pulp (for example, the deinked pulp is employed in a decreased amount for the under surface of cardboard or added in a decreased amount to newspapers). The term "total remaining ink" as used herein means the combined amount of unliberated ink adhering to the deinked pulp and re-adherent ink which has been once liberated from the pulp but adheres thereto again in the deinking step.
The present inventors previously proposed using a reaction product obtained by the addition reaction of an alkylene oxide with a mixture of a natural fat or a product obtained by previously reacting a natural fat with glycerol and a monohydric or polyhydric alcohol as a deinking agent (refer to Japanese Patent Laid-Open Nos. 239585/1985, 293483/1990, 293484/1990, 293485/1990 and 881/1991, and European Patent Publication-A No. 0241224).
Subsequently, the present inventors have examined in detail the behavior of deinking agents obtained in the deinking step. As a result, they have found out that a deinking agent having a mixing molar ratio of a natural fat to a monohydric or polyhydric alcohol of 1:0.3 to 1:3 shows a poor defoaming property in the flotation reject and, as a result, often causes foaming troubles, and that the deinked pulp obtained with the use of this deinking agent is contaminated with a large amount of the total remaining ink, though it has a high whiteness.